Re: VM Host Hardware Recommendations.

Question about CPU cache:

Can you quantify what "large CPU cache" would be?

Thanks
G



On 26 July 2011 09:37, Bart Trojanowski <[email protected]> wrote:

> First and foremost you need a CPU with hardware virtualization
> extensions. I am taking this for granted because it's hard to find a
> server class CPU w/o this.
>
> As Brad pointed out, it's hard to give specific advice until you know
> the I/O vs CPU vs memory load.  However, I can give you some general
> advice.
>
> There are three things I look for when building hosts for virtualization:
>
> - cache
>
> Having a large CPU cache means that context switches (in this case
> from one VM to another) are not as costly.  It also reduces the
> contention on the memory bus, which is a shared between multiple VMs.
>
> - RAM
>
> Naturally more RAM allows you run more VMs... but more importantly
> having lots of RAM prevents the need to go to disk to get data as it
> can be cached.  Having free RAM around can improve certain kind of
> disk I/O loads.  This is true on non-virtualized systems as well.
>
> - cores
>
> If you have a lot of active VMs, the system will spend a lot of time
> ushering VMs in and out of the CPU.  This wastes time, and having more
> cores helps.  Be careful here... adding cores without adding to the
> CPU cache can make things worse.
>
> After these, thing get expensive.  You can pin dedicated network cards
> to each VM to improve network I/O.  You can also improve your storage
> I/O bandwidth by using a SAN.
>
> -Bart
> --
> OCLUG general discussion list
> [email protected]
> http://oclug.on.ca/mailman/listinfo/oclug
>



-- 
- Garth
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